Although there has been considerable development in styrenic polymers, inexpensive polymers using predominantly styrene that are transparent, glossy and which have high impact strength are still sought. Polystyrene, high impact polystyrene, radial block copolymers, and the like, have been developed with various degrees of satisfaction to meet these requirements. But, polymer articles that have satisfactory clarity, such as those made from polystyrene polymers, are lacking in impact strength. Articles formed from blends of polymers, such as high impact polystyrene, often possess the satisfactory impact strength but lack sufficient clarity or other requisite properties. Blends of polystyrene with various compounds such as butadiene-styrene copolymers have been developed but as the impact strength of these plastic articles is increased there is also an increase in the opacity of the article and therefore they too have limited application.
High molecular weight block copolymers of butadiene and styrene containing six or more blocks in which the polymer has a branched (non-linear) configuration and referred to as radial polymers are known and are described in U.S. Pat. Nos. 3,639,517 and 4,091,053. In accordance with this invention, linear high molecular weight block copolymers of styrene and butadiene containing at least five blocks are prepared which have good optical clarity and other desirable physical properties.